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| United States Patent |
5,030,521
|
|
Nishikawa
, et al.
|
July 9, 1991
|
Magnetic recording medium using a fatty acid ester lubricant wherein the
alcohol component is branched at the number one carbon position
Abstract
A magnetic recording medium comprises a nonmagnetic support and a magnetic
recording layer containing a ferromagnetic powder which is provided on the
support. The magnetic recording layer contains a binder resin having a
acid residue or a salt thereof and a fatty acid ester compound having the
formula (I):
##STR1##
wherein R is a hydrocarbon group having 11-21 carbon atoms, R.sup.1 is
hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, and R.sup.2
and R.sup.3 are the same or different and each is a hydrocarbon group
having 1-8 carbon atoms. The total number of carbon atoms contained in
R.sup.1, R.sup.2 and R.sup.3 being not less than 3 carbon atoms.
Alternatively, the fatty acid ester can be coated on the magnetic layer.
| Inventors:
|
Nishikawa; Yasuo (Kanagawa, JP);
Ohya; Takao (Kanagawa, JP);
Miyatsuka; Hajime (Kanagawa, JP)
|
| Assignee:
|
Fuji Photo Film Co., Ltd. (Kanagawa, JP)
|
| Appl. No.:
|
183875 |
| Filed:
|
April 20, 1988 |
Foreign Application Priority Data
| Current U.S. Class: |
428/843.4 |
| Intern'l Class: |
G11B 023/00 |
| Field of Search: |
428/695,694,425.9,900
252/56 R
|
References Cited
U.S. Patent Documents
| 3809652 | May., 1974 | Brennan | 252/56.
|
| 4420540 | Dec., 1983 | Ogawa et al. | 428/457.
|
| 4675250 | Jun., 1987 | Kanai et al. | 428/403.
|
| 4701372 | Oct., 1987 | Akiyama et al. | 428/323.
|
| 4731292 | Mar., 1988 | Sasaki et al. | 428/425.
|
| 4748090 | May., 1988 | Yamamoto et al. | 428/694.
|
| 4786551 | Nov., 1988 | Ootani et al. | 428/323.
|
Primary Examiner: Cashion, Jr.; Merrell C.
Assistant Examiner: Resan; Stevan A.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
We claim:
1. A magnetic recording medium comprising a non-magnetic support and a
magnetic recording layer containing a ferromagnetic powder which is
provided on the support, wherein said magnetic recording layer contains a
binder resin having an acid residue or a salt thereof in its molecular
structure and a fatty acid ester compound having the formula (I):
##STR4##
wherein R is a hydrocarbon group having 11-21 carbon atoms, R.sup.1 is
hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, R.sup.2 and
R.sup.3 are the same or different, each is a hydrocarbon group having 1-8
carbon atoms, and the total number of carbon atoms contained in R.sup.1,
R.sup.2 and R.sup.3 is not less than 3 carbon atoms.
2. The magnetic recording medium as claimed in claim 1, wherein R in the
formula (I) is a hydrocarbon group having 13-17 carbon atoms, R.sup.1 in
the formula (I) is hydrogen or methyl, each of R.sup.2 and R.sup.3 is a
hydrocarbon group having 1-8 carbon atoms.
3. The magnetic recording medium as claimed in claim 1, wherein said
magnetic recording layer contains the fatty acid ester compound of the
formula (I) in an amount of 0.2 to 4.0 wt. % based on the amount of the
ferromagnetic powder.
4. The magnetic recording medium as claimed in claim 1, wherein said
magnetic recording layer contains the fatty acid ester compound of the
formula (I) in an amount of 0.5 to 2.0 wt. % based on the amount of the
ferromagnetic powder.
5. The magnetic recording medium as claimed in claim 1, wherein said acid
residue or a salt thereof is at least one polar group selected from the
group consisting of --SO.sub.3 H, --O--SO.sub.3 H, --PO.sub.2 H.sub.2,
--OPO.sub.2 H.sub.2, --COOH and salt thereof.
6. A magnetic recording medium comprising a non-magnetic support and a
magnetic recording layer containing a ferromagnetic powder wherein said
magnetic layer contains a binder resin having an acid residue or a salt
thereof and a lubricant layer containing a fatty acid ester compound in an
amount of 1 to 500 mg/m.sup.2, the fatty acid ester compound having the
formula (I):
##STR5##
wherein R is a hydrocarbon group having 11-21 carbon atoms, R.sup.1 is
hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, R.sup.2 and
R.sup.3 are the same or different, each is a hydrocarbon group having 1-8
carbon atoms, and the total number of carbon atoms contained in R.sup.1,
R.sup.2 and R.sup.3 is not less than 3 carbon atoms, is provided on the
magnetic recording layer.
7. The magnetic recording medium as claimed in claim 6, wherein R in the
formula (I) is a hydrocarbon group having 13-17 carbon atoms, R.sup.1 in
the formula (I) is hydrogen or methyl, each of R.sup.2 and R.sup.3 is a
hydrocarbon group having 1-8 carbon atoms.
8. The magnetic recording medium as claimed in claim 6, wherein said
lubricant layer contains the fatty acid ester compound of the formula (I)
in an amount of 5 to 150 mg/m.sup.2.
9. The magnetic recording medium as claimed in claim 6, wherein said acid
residue or a salt thereof is at least one polar group selected from the
group consisting of --SO.sub.3 H, --O--SO.sub.3 H, --PO.sub.2 H.sub.2,
--OPO.sub.2 H.sub.2, --COOH and salt thereof.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved magnetic recording medium
comprising a nonmagnetic support and a magnetic recording layer.
2. Description of Prior Art
A magnetic recording medium (hereinafter also referred to as a magnetic
tape) such as an audio tape, a video tape or a recording medium used in a
computer system basically comprises a nonmagnetic support and a magnetic
recording layer provided on the support. The magnetic recording layer
comprises a ferromagnetic powder such as a needle crystalline powder of
.gamma.-Fe.sub.2 O.sub.3, Co-containing ferromagnetic iron oxide or
CrO.sub.2 dispersed in a binder. Recently, a demand for a higher density
recording system has increased, and hence a magnetic recording medium
using a ferromagnetic alloy powder mainly containing metals such as iron,
nickel and cobalt has been widely employed in place of the conventional
oxide-type ferromagnetic powder. The ferromagnetic alloy powder is high in
both of a coercive force (Hc) and a residual flux density (Br), so that a
magnetic recording medium using such powder can afford recording of higher
density. For these reasons, the ferromagnetic alloy powder can be suitably
employed for magnetic recording media of higher density recording system.
Especially in a video tape, requirement for extremely high density
recording has increased in accordance with utilization of measures of
using a short recording wavelength or narrowing track width, and hence the
ferromagnetic alloy powder has been widely used in place of the
conventional oxide-type ferromagnetic powder.
In the case of using the ferromagnetic alloy powder, it is known that much
higher density recording can be attained by smoothening the surface of a
magnetic recording layer containing the ferromagnetic alloy powder, and
thereby the resulting magnetic recording medium can be enhanced in the
electromagnetic conversion characteristics. However, when the surface of
the magnetic recording layer is too smooth, a friction coefficient given
by the contact between the magnetic recording layer and a member of a
recording device increases in the course of running of the recording
medium such as a video tape. As a result, the magnetic recording layer of
the recording medium is apt to be easily damaged or easily separated from
the support even when the recording medium is used for a short period of
time. Particularly, in the case of a video tape, since the video tape runs
at a high speed in contact with a video head, the ferromagnetic powder
tends to easily drop off from the recording layer in the course of running
to cause occurrence of clogging on the head. Accordingly, the magnetic
recording layer of the video tape is desired to be improved in running
durability.
For improving the running durability of the magnetic recording layer, it
has been proposed to incorporate an abrasive (i.e., hard particles) such
as corundum, silicon carbide or chromium oxide into the recording layer.
In this case, however, the effect of incorporation of an abrasive is shown
only where the abrasive is incorporated in a large amount. However, a
magnetic recording layer containing a large amount of an abrasive likely
causes extreme abrasion of a magnetic head employed in contact with the
recording layer. Further, the incorporation of a large amount of an
abrasive into the recording layer is unfavorable from the viewpoint of
enhancement of the electromagnetic conversion characteristics of the
resulting recording medium which are obtained by measures of smoothening
the surface of the recording layer.
It has been also proposed that a lubricant such as a fatty acid or an ester
of a fatty acid and an aliphatic alcohol is incorporated into the
recording layer to lower the above-mentioned friction coefficient.
Now with wide spread of a portable video tape recorder, a video tape is
expected to be employed under severe conditions such as a condition of a
low temperature and a condition of a high temperature and a high humidity.
Therefore, the video tape is required to hardly vary in the running
durability and show stable durability in the course of running even under
such severe conditions. However, the above-mentioned conventional
lubricants hardly improve the running durability of the recording medium
to a satisfactory level.
As described before, a ferromagnetic alloy powder has been widely employed
as a replacement for the conventional ferromagnetic powder with respect to
a video tape or a floppy disc, as the size of such recording medium has
been made smaller for ultization of a short recording wavelength or a
narrow track width. The ferromagnetic alloy powder can relatively improve
the electromagnetic conversion characteristics of the resulting medium but
hardly improves the running durability thereof to a satisfactory level, so
that the magnetic recording medium using such ferromagnetic alloy powder
is desired to be improved in the running endurance.
A magnetic recording layer of a recording medium can be formed on a
nonmagnetic support by a conventional coating method, that is, a method of
coating a magnetic paint comprising a ferromagnetic powder dispersed in a
binder over the support. Otherwise, a magnetic recording layer can be also
formed on the support by a metal deposition method using no binder such as
sputtering, ion plating, electroplating or electroless plating, and
recently, such recording layer prepared by the metal deposition method
(i.e., a metal thin film type-recording layer) has been studied in detail
for practical use. However, the metal thin film type-recording layer has
drawbacks concerning various properties required for magnetic recording
media such as resistance to weather, smooth running property, and
resistance to abrasion (running durability). For example, the metal thin
film type-recording layer having an extremely smooth surface is more
difficult to be provided with high running durability, as compared with
the conventional recording layer of coated type. For this reason, it has
been proposed to further provide a lubricant layer or a protective layer
on such recording layer to improve the running property or to enhance the
running durability.
The protective layer for the metal thin film type-recording layer of a
magnetic recording medium can be formed on the recording layer by coating
an organic solvent solution of a thermoplastic resin, a thermosetting
resin, a fatty acid, a metal salt of fatty acid, a fatty acid ester or an
alkyl phosphoric acid ester over the recording layer, as described in
Japanese Patent Provisional Publications No. 60(1985)-69824 and No.
60(1985)-85427.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording
medium which is improved in both of the electromagnetic conversion
characteristics and the running durability.
Particularly, the invention has an object to provide a magnetic recording
medium having high electromagnetic conversion characteristics and showing
stable and high running durability even when the temperature or the
humidity largely varies, that is, less suffering from influences of
variation of temperature or humidity.
There is provided by the present invention a magnetic recording medium
comprising a nonmagnetic support and a magnetic recording layer containing
a ferromagnetic powder which is provided on the support, characterized in
that said magnetic recording layer further contains a binder resin having
an acid residue or a salt thereof and a fatty acid ester compound having
the formula (I):
##STR2##
wherein R is a hydrocarbon group having 11-21 carbon atoms, R.sup.1 is a
hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, each of
R.sup.2 and R.sup.3 is a hydrocarbon group having 1-8 carbon atoms, and
R.sup.2 and R.sup.3 are the same as or different from each other.
Alternatively, a lubricant layer containing the fatty acid ester compound
of the formula (I) can be provided on the magnetic recording layer.
The magnetic recording medium of the present invention shows high
electromagnetic conversion characteristics. Particularly, when the
recording medium is used as a video tape, the video tape has a long still
life in a still mode and shows high running durability. In addition, the
video tape has a low friction coefficient in a wide temperature range and
hardly brings about clogging on a magnetic head even under condition of
low humidity. When the recording medium is used as a floppy disc, the disc
shows high output as well as high running durability.
DETAILED DESCRIPTION OF THE INVENTION
A magnetic recording medium of the invention essentially comprises a
nonmagnetic support and a magnetic recording layer containing a
ferromagnetic powder which is provided on the support.
As the nonmagnetic support employable in the invention, there can be
mentioned, for example, synthetic resin films such as films of
polyethylene terephthalate, polypropylene, polycarbonate, polyethylene
naphthalate, polyamide, polyamideimide and polyimide, and metallic foils
such as aluminum foil and stainless steel foil. The thickness of the
nonmagnetic support generally is in the range of 3 to 50 .mu.m, preferably
in the range of 5 to 30 .mu.m.
The magnetic recording medium of the invention has a magnetic recording
layer containing a ferromagnetic powder on the nonmagnetic support, as
described above.
The present inventors have studied compounds when used as a lubricant which
can improve the running durability of a magnetic recording medium having
the aforementioned magnetic recording layer of coated type. As a result,
they have found that the magnetic recording medium can be remarkably
improved in its resistance to abrasion in the course of running in contact
with members of a running system, such as a magnetic head and a guide
pole. Also, friction coefficient against such members is significantly
reduced by incorporating the fatty acid ester compound having the above
formula (I) into the magnetic recording layer which contains a binder
resin having an acid residue or a salt thereof in its molecular structure,
or providing a layer of the fatty acid ester compound having the formula
(I) on the magnetic recording layer using the acid residue (or its
salt)-containing binder resin. The possible incorporation of the above
fatty acid compound into a recording layer of a magnetic recording
material is disclosed in Japanese Patent Provisional Publication No.
58(1983)-177526. However, even if the fatty acid ester compound is
incorporated into a conventional magnetic recording layer, the resulting
magnetic recording medium cannot be sufficiently improved in the running
durability. The magnetic layer of the invention contains both the fatty
acid ester compound and the above resin having an acid residue or a salt
thereof. The above binder is supposed to be predominantly adsorbed on the
surface of an inorganic powder such as a ferromagnetic powder owing to
affinity of the acid residue or a salt thereof. As a result, the above
fatty acid ester compound is hardly adsorbed on the surface of the
ferromagnetic powder, so that the compound is apt to be located in the
vicinity of the surface of the magnetic recording layer. Further, when a
layer of the fatty acid ester compound is provided on a magnetic recording
layer, the compound hardly penetrates into the magnetic recording layer
for the same reason as above. Accordingly, the fatty acid ester compound
exhibits sufficient lubricating action on the magnetic recording layer, so
that the magnetic recording medium of the invention shows high running
durability.
There is no specific limitation on the fatty acid ester compound employable
in the invention, provided that the compound has the formula (I):
##STR3##
wherein R is a hydrocarbon group having 11-21 carbon atoms, R.sup.1 is a
hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, each of
R.sup.2 and R.sup.3 is a hydrocarbon group having 1-8 carbon atoms, and
R.sup.2 and R.sup.3 are the same as or different from each other.
In the formula (I), R is preferably a hydrocarbon group having 13-17 carbon
atoms and R.sup.1 is preferably a hydrogen atom or a methyl group.
Examples of the fatty acid ester compounds having the formula (I) are as
follows:
1-methylpropyl stearate, 1,1-dimethylethyl stearate, 1-methylbutyl
stearate, 1-methylheptyl stearate, 1-methylhexyl stearate, 1-methyloctyl
stearate, 1,1-dimethylbutyl stearate, and 1-ethyl-1-methylhexyl stearate;
1-methylpropyl palmitate, 1,1-dimethylethyl palmitate, 1-methylbutyl
palmitate, and 1-methylheptyl palmitate;
1-methylhexyl myristate, 1-methyloctyl myristate, 1,1-dimethylbutyl
myristate, and 1-ethyl-1-methylhexyl myristate;
1-methylpropyl oleate, 1,1-dimethylethyl oleate, 1-methylbutyl oleate,
1,1-dimethylbutyl oleate, and 1-ethyl-1-methylhexyl oleate; and
1-methylpropyl behenate, and 1,1-dimethylethyl behenate.
In the case of a magnetic recording layer of coated type (i.e., a magnetic
recording layer mainly containing a ferromagnetic powder and a binder),
the above-mentioned fatty acid ester compound can be incorporated into the
recording layer or allowed to exist on the recording layer, for example,
by the following three methods:
(1) The fatty acid ester compound is added to a magnetic paint for the
formation of a magnetic recording layer.
(2) A layer of the fatty acid ester compound is provided on a surface of a
nonmagnetic support prior to forming the recording layer.
(3) A layer of the fatty acid ester compound is provided on a surface of a
magnetic recording layer after the recording layer is formed on the
support.
The method (2) for providing a layer of the fatty acid ester compound
between the magnetic recording layer and the support is a little inferior
to other methods (1) and (3) from the viewpoint of the effect given by the
present invention.
As the method (3), there can be utilized a method of coating or spraying an
organic solvent solution of the fatty acid ester compound over the
magnetic recording layer, and a method of subjecting the fatty acid ester
compound to adsorption on the recording layer. In the adsorption method,
the compound per se may be adsorbed by the surface of the recording layer
or the recording layer may be immersed in an organic solvent solution of
the compound (i.e., Langmuir Blodgett technique). In the method (3), the
layer of the fatty acid ester compound can be provided on the recording
layer at any desired time, for example, immediately after the magnetic
paint is coated, while the coated layer of the magnetic paint is wet,
after the coated layer of the magnetic paint is dried, after subjecting
the magnetic recording layer to surface smoothening treatment, or after
subjecting the magnetic recording layer to other mechanical treatment such
as grinding treatment.
In the method (1) for adding the fatty acid ester compound to a magnetic
paint for the formation of a coated type-magnetic recording layer, the
amount of the fatty acid ester compound employable in the invention is
preferably in the range of 0.2 to 4.0 wt. %, more preferably 0.5 to 2.0
wt. %, based on the ferromagnetic powder contained in the magnetic paint.
In the method (2) for providing a layer of the fatty acid ester compound
between the coated type-recording layer and the support, the amount of the
compound (i.e., amount of the compound existing in the coated layer
thereof after dryness) is preferably in the range of 10 to 200 mg/m.sup.2.
In the method (3) for providing a layer of the fatty acid ester compound
on the surface of the coated type-recording layer not facing the support,
the amount of the compound is preferably in the range of 1 to 500
mg/m.sup.2, more preferably 5 to 150 mg/m.sup.2.
There is no specific limitation on the ferromagnetic powder employable in
the invention. Examples of the ferromagnetic powder include a
ferromagnetic alloy powder, a ferromagnetic metal powder mainly containing
iron, an iron oxide type ferromagnetic powder such as .gamma.-Fe.sub.2
O.sub.3 and Fe.sub.3 O.sub.4, and a modified iron oxide type ferromagnetic
powder such as Co-containing iron oxide, modified barium ferrite and
modified strontium ferrite.
As the ferromagnetic metal powder, there can be mentioned a ferromagnetic
alloy powder containing a metal component of at least 75 wt. % in which at
least 80 wt. % of the metal component comprises at least one ferromagnetic
metal or metal alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni, Co-Ni, or Co-Ni-Fe)
and the remaining metal component, if present, comprises other atom(s)
(e.g., Al, Si, S, Sc, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, Rh, Pd, Ag, Sn, Sb,
Te, Ba, Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, B, or P). The
ferromagnetic metal component may contain a small amount of water,
hydroxide, or oxide. These ferromagnetic metal powders are already known,
and can be prepared by known methods.
There is no specific limitation on the shape of the ferromagnetic metal
powder employable in the invention, and normally used is needle shape,
grain shape, dice shape, rice shape or plate shape.
The binder employable for the formation of the magnetic recording layer of
the invention can be selected from known resins such as thermoplastic
resins, thermosetting resins, and reactive resins. These resins can be
employed singly or in combination.
The thermoplastic resin employable in the invention generally has a mean
molecular weight of 10,000 to 200,000 and a polymerization degree of
approx. 200 to 2,000. Examples of the thermoplastic resin include vinyl
chloride/vinyl acetate copolymer resins (e.g., vinyl chloride/vinyl
acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer
and vinyl chloride/vinyl acetate/maleic anhydride copolymer), vinyl
chloride/vinylidene chloride copolymer resins, acrylic resins (e.g., vinyl
chloride/acrylonitrile copolymer, vinylidene chloride/acrylonitrile
copolymer, (meth)acrylic acid ester/acrylonitrile copolymer, (meth)acrylic
acid ester/vinylidene chloride copolymer, (meth)acrylic acid ester/styrene
copolymer and butadiene/acrylonitrile copolymer), cellulose derivatives
(e.g., cellulose acetate butyrate, cellulose diacetate, cellulose
triacetate, cellulose propionate, cellulose acetate propionate,
nitrocellulose and cellulose acetate), a variety of thermoplastic resins
of synthetic rubber type (e.g., polybutadiene, chloroprene, polyisoprene
and styrene butadiene copolymer), polyurethane resins, polyvinyl fluoride
resins, polyamide resins, polyvinyl butylate resins, styrene/butadiene
copolymer resins and polystyrene resins.
The thermosetting resin or the reactive resin employable in the invention
generally has a mean molecular weight of not more than 200,000 in the
state of a component of a coating dispersion, and the molecular weight of
those resins becomes infinity after being coated through condensation
reaction or addition reaction. Preferably employable thermosetting resin
is one which does not soften or melt under heating in the course of
hardening. Examples of such resins include phenol/formalin/novolak resin,
phenol/formalin/resol resin, phenol/furfural resin, xylene/formalin resin,
urea resin, melamine resin, drying oil alkyd resin, phenolic resin
modified alkyd resin, maleic resin modified alkyd resin, unsaturated
polyester resin, a mixture of epoxy resin and hardening agent such as
polyamine, acid anhydride and polyamide resin, isocyanate polyether
moisture-cure type resin, polyisocyanate prepolymer (e.g., a reaction
product of diisocyanate and low-molecular triol containing three or more
isocyanate groups in one molecule, and trimer or tetramer of
diisocyanate), and a mixture of polyisocyanate prepolymer and a resin
having active hydrogen (e.g., polyester polyol, polyether polyol, acrylic
acid copolymer, maleic anhydride copolymer, 2-hydroxyethyl methacrylate
copolymer, and p-hydroxystyrene copolymer).
Preferably employed as the binder is a combination of the vinyl
chloride/vinyl acetate copolymer and the polyurethane resin which further
contains a cellulose derivative.
As described hereinbefore, from the viewpoint of dispersing power and
running durability of the resulting recording layer, the above-mentioned
resin is required to have an acid residue such as --SO.sub.3 H,
--O--SO.sub.3 H, --PO.sub.2 H.sub.2, --OPO.sub.2 H.sub.2 or --COOH, or
salt thereof such as --SO.sub.3 Na or --O--SO.sub.3 Na, in its molecular
structure, and further may have hydroxyl group, an epoxy group or an amino
group in the molecular structure.
The amount of the binder is generally in the range of 10 to 100 parts by
weight, preferably in the range of 15 to 50 parts by weight, per 100 parts
by weight of the ferromagnetic powder.
The magnetic recording layer of the magnetic recording medium according to
the invention preferably further contains an inorganic powder having a
Mohs' scale of hardness of not less than 5.
There is no specific limitation on the inorganic powder employable in the
invention, provided that the powder has a Mohs' scale of hardness of not
less than 5. Examples of the inorganic powder having a Mohs' scale of
hardness of not less than 5 include Al.sub.2 O.sub.3 (Mohs' scale of
hardness: 9), TiO.sub.2 (said hardness: 6.5), SiO.sub.2 (said hardness:
7), SnO.sub.2 (said hardness: 6.5), Cr.sub.2 O.sub.3 (said hardness: 9),
and .alpha.-Fe.sub.2 O.sub.3 (said hardness: 5.5). Preferred is an
inorganic powder having a Mohs' scale of hardness of not less than 8. If
an inorganic powder having a Mohs' scale of hardness of less than 5 is
employed, the powder easily drops off from the magnetic recording layer
and hardly has a function of abrasion for a magnetic head but causes
clogging on the head, whereby the resulting recording medium deteriorates
in the running durability.
The inorganic powder is contained in the magnetic recording layer in an
amount of generally 0.1 to 20 parts by weight, preferably 1 to 10 parts by
weight, based on 100 parts by weight of the ferromagnetic powder. The
magnetic recording layer desirably contains carbon black (preferably
having a mean particle size of 10-300 m.mu.), etc. other than the
above-mentioned components.
A process for the preparation of a magnetic recording medium of the present
invention is described hereinafter, referring to a process comprising
adding the above-mentioned fatty acid ester compound to a magnetic paint
form forming a magnetic recording layer.
In the first place, the above-described ferromagnetic powder, binder, fatty
acid ester compound, and if necessary other additives such as a lubricant
or a filler are kneaded with an appropriate solvent to prepare a magnetic
paint (or dispersion). The solvent employable in the invention is a known
solvent used for the preparation of the conventional magnetic paint such
as methyl ethyl ketone. The kneading procedure can be carried out by a
known method conventionally used for the preparation of a magnetic paint.
The order of addition of each component for the preparation of a magnetic
paint can be appropriately selected. The magnetic paint can be prepared
using a known kneading apparatus such as a two-roll mill, a three-roll
mill, a ball mill, a pebble mill, a Tron mill, a sand grinder, a Szegvali
attritor, a high-speed impeller dispersing apparatus, a high-speed stone
mill, a high-speed impact mill, a disperser, a kneader, a high-speed
mixer, a homogenizer and a ultrasonic dispersing apparatus.
In the preparation of a magnetic paint, other additives such as a
dispersing agent and an antistatic agent can be also employed in
combination with the above-mentioned components.
Examples of the dispersing agent employable in the invention include a
fatty acid having 12-18 carbon atoms (e.g., caprylic acid, capric acid,
lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,
elaidic acid, linolic acid, linolenic acid and stearolic acid), a metallic
soap composed of an alkali metal such as lithium, sodium or potassium and
an alkaline earth metal such as magnesium, calcium or barium, a compound
thereof in which at least one hydrogen is substituted by a fluorine atom,
amide of the above-mentioned fatty acid, aliphatic amine, higher alcohol,
polyalkylene oxide alkyl phosphoric acid ester, alkyl phosphoric acid
ester, alkyl boric acid ester, sarcosinates, alkyl ether esters, trialkyl
polyolefin oxyquaternary ammonium salt and lecithin. The dispersing agent
is generally used in an amount of 0.1 to 10 parts by weight per 100 parts
by weight of the employed binder.
Examples of the antistatic agent employable in the invention include
conductive powders such as carbon black and carbon black grafted polymer;
natural surfactants such as saponin; nonionic surfactants of alkylene
oxide type, glycerol type or glycidol type; cationic surfactants such as
higher alkylamines, quaternary ammonium salts, salts of pyridine or other
heterocyclic compound, phosphonium and sulfonium; anionic surfactants
containing acid group such as carboxylic acid, sulfonic acid, phosphoric
acid, sulfuric acid ester group and phosphoric acid ester group; and
amphoteric surfactants such as amines, aminosufonic acids, sulfuric acid
ester or phosphoric acid ester of amino alcohol. In the case of using the
conductive powder as an antistatic agent, the amount of the conductive
powder is generally in the range of 0.1 to 10 parts by weight per 100
parts by weight of the employed binder. In the case of using the
surfactant as an antistatic agent, the amount of the surfactant is
generally in the range of 0.12 to 10 parts by weight per 100 parts by
weight of the employed binder.
In the invention, it is also possible to use various lubricants in the
preparation of a magnetic paint in combination with the above-described
components. Examples of the lubricants include known solid powders such as
a graphite powder, a molybdenum disulfide powder and a teflon powder, a
small amount of higher alcohol, sorbitan oleate, mineral oils, animal
oils, vegetable oils, olefin low polymers, and .alpha.-olefin low
polymers.
The above-mentioned additives such as a dispersing agent and an antistatic
agent are by no means given under the restriction that those additives
strictly have only the above-described functions. For example, the
dispersing agent sometimes serves as an antistatic agent. Accordingly, it
should be understood that the functions of the compounds exemplified above
are by no means restricted to those classified above. In the case of using
an additive having plural functions, the amount of the additive is
determined under the consideration of those plural functions.
In the second place, the magnetic paint prepared as above is coated on a
surface of the aforementioned non-magnetic support. Generally, a magnetic
recording layer is formed by coating the magnetic paint directly on the
nonmagnetic support, but it is also possible to provide an adhesive layer
or a subbing layer between the magnetic paint layer and the nonmagnetic
support. The coating procedure can be performed according to a
conventional coating method such as an air doctor coating, a blade
coating, a rod coating, an extrusion coating, an air knife coating, a
squeeze coating, an impregnation coating, a reverse roll coating, a
transfer roll coating, a gravure coating, a kiss coating, a cast coating,
a spray coating and a spin coating. Other coating methods can be also
applied to the present invention.
The magnetic recording layer provided on the surfaces of the nonmagnetic
support has a thickness (thickness in dry state) generally in the range of
approx. 0.5 to 10 .mu.m, preferably in the range of 1.5 to 7.0 .mu.m.
The magnetic recording layer provided on the nonmagnetic support is
generally subjected to orienting the ferromagnetic powder contained in the
magnetic recording layer, that is, a magnetic orientation, in the case
that the resulting magnetic recording medium is used in the form of a
tape, and then subjected to a drying process. If necessary, the surface of
the magnetic recording layer is subsequently subjected to a smoothening
process. The obtained sheet is then cut or slit into a desired shape.
The examples and the comparison examples of the present invention are given
below. In the following examples, the expression "parts" means "parts by
weight", unless otherwise specified.
EXAMPLES 1-7
______________________________________
Composition of Magnetic Paint
______________________________________
Ferromagnetic metal powder (Fe--Zn--Ni alloy,
100 parts
Fe: 94 wt. %, Zn: 4 wt. %, Ni: 2 wt. %,
coercive force (Hc): 700 Oe,
specific surface area (S-BET): 30 m.sup.2 /g)
Vinyl chloride/vinyl acetate/maleic
15 parts
anhydride copolymer
(VMCH of Union Carbide Co., Ltd.
containing about 2 wt. % of maleic acid)
Polyurethane resin 10 parts
(Niporan N2304, available from
Nippon Polyurethane Co., Ltd.)
Lecithin 3 parts
Oleic acid 2 parts
Octyl laurate 5 parts
Lauric acid 5 parts
Fatty acid ester compound
(kind and amount are indicated in Table 1)
Carbon black (mean diameter: 20 nm)
5 parts
Butyl acetate 300 parts
Methyl ethyl ketone 300 parts
______________________________________
The above-listed components were kneaded in a ball mill for 48 hours. To
the mixture was added 5 parts of polyisocyanate and the mixture was again
kneaded for one hour to give a dispersion. The dispersion was filtered
over a filter having a pore size of 1 .mu.m to prepare a magnetic paint.
The magnetic paint was coated on a surface of a polyethylene terephthalate
support (thickness: 10 .mu.m) to give a coated layer of the magnetic paint
having thickness of 4.0 .mu.m (thickness in dry state).
The support with the coated layer was treated with an electromagnet at
3,000 gauss under wet condition to give a magnetic orientation. After the
coated layer was dried, the layer was subjected to supercalendering. The
resulting sheet was slit to give a video tape having a width of 1 inch.
TABLE 1
______________________________________
Amount
Fatty Acid Ester Compound
(by weight)
______________________________________
Example 1
1-methylpropyl stearate
1.5 parts
Example 2
" 1.0 part
Example 3
" 0.8 part
Example 4
1,1-dimethylethyl oleate
2.0 parts
Example 5
1-ethyl-1-methylhexyl myristate
1.5 parts
Example 6
1-methylbutyl stearate
1.5 parts
Example 7
1,1-dimethylbutyl oleate
1.5 parts
______________________________________
EXAMPLES 8-12
The procedures of Examples 1-5 were repeated except for replacing the two
binder resins with a combination of 15 parts of vinyl chloride/vinyl
acetate copolymer (VAGH of Union Carbide Co., Ltd.) and 10 parts of
polyester polyurethane resin (obtained by ring-opening and condensation
polymerization, weight-average molecular weight: 40,000, number-average
molecular weight: 20,000) having two --SO.sub.3 Na groups on average in
one molecule) to prepare video tapes of Examples 8-12, respectively.
COMPARISON EXAMPLES 1-5
The procedures of Examples 1-5 were repeated except for replacing the vinyl
chloride/vinyl acetate/maleic anhydride copolymer with the same amount of
vinyl chloride/vinyl acetate (VAGH of Union Carbide Co., Ltd.) to prepare
video tapes of Comparison Examples 1-5, respectively.
The video tapes obtained in the above-described examples were evaluated on
the reproduction output sensitivity of radio frequency (RF) signal,
lowering of output and friction coefficient according to the following
tests.
REPRODUCTION OUTPUT SENSITIVITY OF RF SIGNAL
A video signal of 50IRE (The institute of Radio Engineers) was recorded on
the video tape at a standard recording current using a 1-inch type video
tape recorder (BVH1000 of Sony Corp., Ltd.). The recorded signal was
reproduced to measure an average value of envelopes of the reproduction
output of RF signal by means of an oscilloscope. The reproduction output
sensitivity of RF signal was determined by introducing the obtained
average value into the following formula:
##EQU1##
in which V means an average value and V.sub.O means a standard value.
LOWERING OF OUTPUT
A signal was recorded on the video tape for 60 minutes at 25.degree. C. and
80% RH using the same video tape recorder as described above, and the
recorded signal was repeatedly reproduced at 100 times to measure the
reproduction outputs. The value of the reproduction output set forth in
Table 2 is a relative value of reproduction output measured at the last
reproduction of 100 times reproductions based on the output measured at
the first reproduction being 0 dB.
Friction Coefficient
The video tape was brought into contact with a stainless pole at a contact
angle of the tape and the pole of 180.degree. under a tension of 50 g.
(T.sub.1) applied to the tape. Under such condition, a tension required
for running the video tape at a speed of 3.3 cm/sec (T.sub.2) was
measured. A friction coefficient (.mu.) of the video tape was determined
by introducing the values of T.sub.1 and T.sub.2 into the following
formula:
Friction coefficient (.mu.)=1/.pi..multidot.ln(T.sub.2 /T.sub.1)
The test for measuring the friction coefficient was carried under the
conditions of a temperature of 23.degree. C. and a humidity of 10% RH.
The results on the above-described evaluations are set forth in Table 2.
TABLE 2
______________________________________
Reproduction Output Lowering
Sensitivity of RF Friction of Output
Signal (dB) Coefficient
(-dB)
______________________________________
Example 1
+1.5 0.22 <1
Example 2
+1.0 0.21 <1
Example 3
+1.0 0.20 <1
Example 4
+1.0 0.23 <1
Example 5
+1.0 0.23 <1
Example 6
+1.0 0.21 <1
Example 7
+1.0 0.21 <1
Example 8
+2.0 0.21 <1
Example 9
+1.5 0.20 <1
Example 10
+1.0 0.20 <1
Example 11
+1.0 0.22 <1
Example 12
+1.0 0.22 <1
Com. Ex. 1
0 0.28 2
Com. Ex. 2
0 0.27 2
Com. Ex. 3
0 0.27 3
Com. Ex. 4
0 0.31 2
Com. Ex. 5
0 0.32 2
______________________________________
EXAMPLES 13-16
______________________________________
Composition of Magnetic Paint
______________________________________
Ferromagnetic metal powder (Fe--Zn--Ni alloy,
100 parts
Fe: 94 wt. %, Zn: 4 wt. %, Ni: 2 wt. %,
coercive force (Hc): 1,500 Oe,
specific surface area (S-BET): 54 m.sup.2 /g)
Vinyl chloride/vinyl acetate/maleic
15 parts
anhydride copolymer
(400 .times. 110A, polymerization degree: 400,
available from Nippon Zeon Co., Ltd., having
--COOH group in the molecule)
Polyester polyurethane resin
8 parts
(obtained by ring opening and condensation
polymerization,
weight-average molecular weight: 40,000,
number-average molecular weight: 20,000,
having two --SO.sub.3 Na groups on average in one
molecule)
.alpha.-Alumina 5 parts
abrasive, mean diameter: 0.2 .mu.m)
Stearic acid 1 part
Oleic acid 0.5 part
Carbon black (mean diameter: 40 nm)
2 parts
Methyl ethyl ketone 300 parts
______________________________________
The above-listed components were kneaded in a ball mill for 48 hours. To
the mixture was added 5 parts of polyisocyanate, and the mixture was again
kneaded for one hour to give a dispersion. The dispersion was filtrated
over a filter having a pore size of 1 .mu.m to prepare a magnetic paint.
The magnetic paint was coated on a surface of a polyethylene terephthalate
support (thickness: 10 .mu.m) to give a coated layer of the magnetic paint
having thickness of 4.0 .mu.m (thickness in dry state).
The support with the coated layer was treated with an electromagnet at
3,000 gauss under wet condition to give a magnetic orientation. After the
coated layer was dried, the layer was subjected to supercalendering.
Independently, a fatty acid ester compound indicated in Table 3 was
dissolved in n-hexane to prepare a solution. The solution was coated over
the layer of the magnetic paint, and the coated layer of the solution was
dried. The resulting sheet was slit to give a video tape having a width of
8 mm.
TABLE 3
______________________________________
Amount
Fatty Acid Ester Compound
(mg/m.sup.2)
______________________________________
Example 13 1 methylpropyl stearate
5
Example 14 " 15
Example 15 1,1-dimethylethyl oleate
20
Example 16 1-methylbutyl stearate
15
______________________________________
COMPARISON EXAMPLES 6-8
The procedures of Examples 13-15 were repeated except for replacing the two
binder resins with a combination of 15 parts of vinyl chloride/vinyl
acetate copolymer (VAGH of Union Carbide Co., Ltd.) and 10 parts of a
polyurethane resin (Niporan NM-2304) to prepare video tapes of Comparison
Example 6-8, respectively.
The video tapes obtained in the above-described examples were evaluated on
lowering of the reproduction output and the friction coefficient according
to the above-mentioned test procedure.
The results of evaluations on lowering of output and friction coefficient
are set forth in Table 4.
TABLE 4
______________________________________
Lowering of Output
Friction Coefficient
(-dB)
______________________________________
Example 13 0.22 <1
Example 14 0.21 <1
Example 15 0.20 <1
Example 16 0.23 <1
Com. Ex. 6 0.28 2
Com. Ex. 7 0.27 3
Com. Ex. 8 0.27 3
______________________________________
As is evident from the results set forth in Tables 1 to 4, each of the
video tapes using the fatty acid ester compound according to the invention
(Examples 1 to 16) showed high reproduction output, and was improved in
both of running property and running durability.
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